Hydraulic system

ABSTRACT

A hydraulic system comprising a pair of hydraulic motors or rams mechanically and hydraulically connected in opposition to each other and control means for simultaneously operating the rams either in tandem or in opposite sense to each other is disclosed. Various embodiments of the control means are described and a wheeled vehicle embodying the hydraulic system is disclosed.

United States Patent Beck [54] HYDRAULIC SYSTEM [72] Inventor: Eugene F. Beck, 29800 Seaview Road, Cazadero, Calif. 95421 [22] Filed: Sept. 8, 1971 [21] Appl. No.: 178,738

Related US. Application Data [63] Continuation-impart of Ser. No. 37,702, May

[52] US. Cl. ..60/52 S, ISO/79.2 B, 60/545 R, 60/97 L, 91/171 [51] Int. Cl ..FlSb 11/22 [58] Field of Search ...60/97 L, 52 S, 54.5 R; 91/171; 280/6 H, 36 R; 180/41, 79.2 B

[56] References Cited UNITED STATES PATENTS 2,229,530 1/1941 South ...9l/l71 X Oct. 24, 1972 5/1970 Bauer ..60/54.5 R X Primary Examiner-Edgar W. Geoghegan Attorney-Oscar A. Mellin et al.

57 ABSTRACT A hydraulic system comprising a pair of hydraulic motors or rams mechanically and hydraulically connected in opposition to each other and control means for simultaneously operating the rams either in tandem or in opposite sense to each other is disclosed. Various embodiments of thecontrol means are described and a wheeled vehicle embodying the hydraulic system is disclosed.

13 Claims, 10 Drawing Figures Van Winsen ..280/6 R PATENTED net 24 I972 SHEET 1 [IF 6 FIG... 1

FIG 2 INVENTOR EUGENE F. BECK BY W *W ATTORNEYS PATENTED 24 I972 3 699 .676

sum '2 0F 6 AUTOMATIC MANUAL CONTROL INVE R EUGENE E BE BY M), MEW

ATTORNEYS PATENTEDUCT 24 m2 SHEET 3 BF 6 QEDQ mm INVENTOR EUGENE F. BECK ATTORNEYS PATENTED 24 I973 3 699 .676

sum 5 or 6 RESERVOIR- PUMP RESERVOIR RESERVOIR INVENTOR. EUGENE F. BECK- MR Mr" V ATTORNEYS PATENTED URI 24 I972 SHEET 5 BF 6 OH O ' INVENTOR. EUGENE F. BECK hea m ATTOR N EYS 1 HYDRAULIC SYSTEM CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of co-pending patent application Ser. No. 37,702, filed May 15, 1970, entitled Wheeled Vehicle Including Hydraulic Leveling System.

BACKGROUND OF THE INVENTION This invention relates to hydraulic systems and more particularly to hydraulic systems in which a pair of hydraulic motors or rams operate in opposite sense to each other to achieve a desired positioning of an elernent, member or device mechanically connected thereto.

There are many applications in which it is desired to control the orientation or positioning of some element, member or device through the action of hydraulic motors. For example, a hydraulic motor or ram has been used between each wheel and the ,frame of wheeled vehicles in order to enable the position of the wheels to be varied vertically with respect to the frame and thereby maintain the frame level on uneven or sloping terrain. In order to maintain the frame at a given average height above the terrain it is, of course, necessary to operate certain of the hydraulic rams in opposite sense to the others. In other words, pressure is applied to certain of the hydraulic rams and, simultaneously, pressure on other hydraulic rams is released. Unfortunately, in such a system the forces involved are not balanced with the result that hunting and exhaustion will inherently occur unless corrected by I skillful manual operation. Hunting means that the system will overreact when a particular change in the orientation is sought, requiring a counter-change to correct the first overreaction and resulting in a further opposite overreaction, so that an oscillation will occur about the desired new orientation until the system eventually stabilizes. Exhaustion means that upon each change in orientation, one of the rams will react to a greater extend than the other ram so that after repeated changes in orientation one or both of the rains will eventually reach the limit of its ability to react again. These effects are particularly pronounced in systems designed to provide automatic control over the rams to maintain a particular orientation of an element, member or device, under conditions involving changing forces thereon.

Thus, considering the example of a wheeled vehicle given above, assume that it is desired to maintain the transverse dimension of the vehicle level. Under such conditions, the hydraulic rams of each pair of wheels on opposite sides of the vehicle frame would be operated in opposite sense to each other so that one extends when the other contracts in order to maintain the transverse dimension of the vehicle level on sloping or uneven terrain. However, the weight of the vehicle will tend to be unevenly distributed between the pair of wheels, particularly during the time when the hydraulic rams are acting to correct for a changed condition in the terrain. The net result of the uneven distribution of weight will be that one of the rams will overreact with respect to the other ram resulting in both hunting and exhaustion as described above.

It is an object of this invention to provide an improved hydraulic system comprising a pair of hydraulic motors or rams mechanically and hydraulically connected in opposition to each other whereby hunting and exhaustion effects are reduced.

It is a further object of this invention to provide an automatically controlled hydraulic system comprising a pair of hydraulic motors or rams mechanically and hydraulically connected in opposition to each other whereby hunting and exhaustion effects are reduced.

It is another object of this invention to provide an improved hydraulic system for automatically maintaining a wheeled vehicle in substantially a selected orientation with respect to the horizontal when operated on sloping or uneven terrain.

It is yet another object of this invention to provide an improved wheeled vehicle for use in providing motive power on uneven or sloping terrain.

It is a still further object of this invention to provide improved control means for operating in opposite sense to each other a pair of double-acting hydraulic rams mechanically and hydraulically connected in opposition to each other.

SUMMARY OF THE INVENTION Briefly, a hydraulic system in accordance with this invention comprises a pair of double-acting hydraulic BRIEF DESCRIPTION OF THE DRAWINGS This invention will be more fully understood from the following detailed description of preferred embodiments thereof when read in conjunction with the drawing wherein:

FIG. 1 is a side view in elevation of a wheeled vehicle including a hydraulic system in accordance with the.

teaching of this invention.

FIG. 2 is a simplified top plan view of the wheeled vehicle shown in FIG. 1 in which portions of the superstructure have been omitted for ease in understanding this invention. 7

FIG. 3 is a fragmentary perspective view of a portion of the wheeled vehicle 25 shown in FIG. 2 with portions of the hydraulic system of this invention indicated diagrammatically.

FIG. 4 is a piping diagram of a hydraulic system in accordance with one embodiment of this invention.

FIG. 5 is a piping diagram of a hydraulic system in accordance with another embodiment of this invention.

FIG. 6 is a fragmentary cross-sectional view taken along line 6-6 of FIG. 5.

FIG. 7 is a view in elevation of a pendulum mechanism which may be used in accordance with the teaching of this invention.

FIG. 8 is a view taken along lines 8-8 of FIG. 7.

FIG. 9 is a piping diagram of a hydraulic system in accordance with a further embodiment of this invention.

FIG. is a schematic diagram of the hydraulic system of FIG. 9 including symbols representative of the functions of certain elements of the system.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, a wheeled vehicle on which a hydraulic system in accordance with the teaching of this invention may be used to advantage is shown. Such wheeled vehicle comprises an articulated frame indicated generally at 10. Such articulated frame comprises a first portion consisting of three sections 11, 12 and 13 and a second portion consisting of section 14. Sections 11 and 12 are directly interconnected mechanically by an articulation joint 15 adapted for horizontal rotation. The third section 13 of the first portion of the frame is mechanically interconnected with sections 11 and 12 by means of the superstructure 16 of the wheeled vehicle and the other portion 14 of the frame is interposed between such third section 13 and the section 12 of the first portion of the frame and mechanically interconnected therewith by means of oscillation joints 17 and 18 adapted for vertical rotation. A first pair of wheels 21 and 22 are mounted on section 11 of the first portion of the frame and a second pair of wheels 23.and 24 are mounted on section 14 comprising the other portion of such frame 10. Thus it will be seen that the vehicle may be steered by means of a hydraulic ram 19 mechanically interposed between sections 11 and 12 of the first portion of the frame 10 and adapted to cause such sections 11 and 12 to pivot horizontally with respect to each other about the vertical axis of the articulation joint 15. Similarly it will be seen that the second portion of the frame 10 comprising section 14 may pivot vertically with respect to the first portion of the frame 10 about the horizontal axis of the oscillation joints 17 and l8-thereby preventing the frame 10 from being subjected to undesirable longitudinal twisting forces which would otherwise occur between the pairs of wheels when the vehicle is operated on uneven or sloping terrain.

As shown in FIGS. 1 and 2, the wheels 21 and 22 of the first pair of wheels and the wheels 23 and 24 of the second pair of wheels are mounted on the frame 10 by means of mutually independent rocker arms 25 and 26. Such rocker arms are pivotally mounted on the frame at one end thereof and have a wheel journalled thereon at the other end thereof. A chain drive mechanism may be disposed in such arms to transmit power available at the end thereof which is pivoted to the frame 10 (e.g. from a differential as indicated at 20) to the wheels which are journalled at the opposite end thereof. As is best shown in FIG. 1, each of such arms 25 and 26 may be caused to pivot with respect to the frame 10 by means of hydraulic rams 27 or 28, respectively, which are connected between the frame and a rigid lever arm indicated at 29 which is affixed to each of such arms 25 and 26. It will be understood that if the rams 27 shown in FIG. 1 are extended, the arms 25 will be caused to pivot downwardly, driving the wheel 21 or 23 downwardly with respect to the frame and thereby tending to elevate one side of the frame with respect to the terrain upon which the wheels rest. Similarly, if the rams 27 are retracted, the arms 25 will be pivoted upwardly with respect to the frame 10, thereby tending to lower one side of the frame with respect to the terrain The rams 28 acting on the rocker rams 26 produce the same effect on the opposite side of the frame 10.

In accordance with this invention, the rams 27 and 28 are double-acting rams and may be hydraulically driven either in opposition to each other or in tandem with each other from a common source of pressurized fluid through a hydraulic control means indicated generally at 30. Thus in accordance with the teaching of this invention, the frame 10 may be raised or lowered with respect to the terrain by operating the cylinders 27 and 28 in tandem and a particular orientation of the frame with respect to the terrain at a given average height therefrom may be obtained by operating the cylinders 27 and 28 in opposition to each other. Such operation will be more fully understood by reference to FIG. 3.

Referring to FIG. 3, a fragmentary perspective view of the frame of a vehicle as described in connection with FIGS. 1 and 2 is shown together with elements of a hydraulic system in accordance with this invention. The reference numerals of FIGS. 1 and 2 have been used in FIG. 3 to indicate common parts or elements. As shown in FIG. 3 a source of pressurized fluid indicated generally at 31 and comprising a hydraulic pump 32 and a reservoir for hydraulic fluid 33 may be mounted on any section of the frame, for example section 12. The pump 32 may be driven by the prime power source (nor shown) of the vehicle by means well known in the art, in order to provide hydraulic fluid to an appropriate distribution system 34 at a pressure at least sufficient to support the weight of the vehicle by means of hydraulic rams 27 and 28. For example, a wheeled vehicle in which the hydraulic system of this invention may be used to advantage may have a total loaded weight in operation approaching 12 tons. If hydraulic rams 27 and 28 have a cylinder diameter of 8 inches, for example, and if theratio of the length of the rocker arms 25 and 26 to the rigid lever arms 29 is 4 to l, for example, a pressure of some 2,000 lbs. per sq. inch would be required to support the entire weight of the vehicle on one of the rams. However, in operation, the weight of the vehicle will always tend to be distributed among the fourwheels thereof so that a substantially lower pressure, for example 1,000 1,500 lbs. per sq. inch will be sufficient for normal operating conditions. A connection to the reservoir 33 for various parts of the hydraulic system is provided through a distribution means 35.

As shown in FIG. 3, a dual connection is made between the hydraulic control means 30 in accordance with this invention and the pump 32 and reservoir 33 through a pair of four-way valves 36 and 37. One of such valves 36 is utilized to cause the hydraulic control system 30 to operate the hydraulic rams 27 and 28 in an opposite sense to each other, whereas the other four-way valve 37 is used to cause the hydraulic control system 30 to operate the rams 27 and 28 in tandem with each other as will be more fully described hereinafter. Appropriate four-way valves for use in the hydraulic system in accordance with this invention are known in the art. The function of such valves is to enable pressurized fluid to be supplied to a selected one of a pair of hydraulic lines while the other of such pair of hydraulic lines is connected to the reservoir. Such valves may be mechanically, hydraulically, pneumatically or electrically actuated by any appropriate control means 38, 39. As shown in FIG. 3, the four-way valve 36 which is utilized in operating the rams 27 and 28 in opposite sense to each other may be automatically controlled by an appropriate device 38 and the four-way valve 37 which is utilized tooperate rams 27 and 28 in tandem may be manually controlled by an appropriate device 39. However, it will be understood that both of such four-way valves may be automatically controlled, manually controlled or provided with a combination automatic/manual control.

Referring to FIG. 4, the details of a hydraulic control means 30 in accordance with one embodiment of this invention are shown diagrammatically. In FIG. 4 the rocker arms 25 and 26 together with the associated double-acting hydraulic rams 27 and 28 and the hydraulic connection of such rams to the control means 30 are indicated diagrammatically. In addition the fourway valves 36 and 37 together with their hydraulic connections to the control means 30 and to thepump and reservoir are indicated diagrammatically. Finally, an electrical automatic control for the four-way valve 36 is indicated schematically. As shown in FIG. 4, a simple manual control 39 is mounted directly on the four-way valve 37.

The hydraulic control means 30 according to this embodiment of the invention comprises a heavy-duty control frame 40 in the form of a hollow box made of heavy gauge steel. A pair of double-acting hydraulic rams 41 and 42 are mounted within the frame 40 in the manner to be described hereinafter. A pair of hydraulic lines connect the ram 41 tothe ram 27 and a second pair of hydraulic lines connect the ram 42 to the ram 28 as shown. The ram 41 and the ram 27 as well as the pair of hydraulic lines extending therebetween are completely filled with hydraulic fluid. Thus, any movement of the piston of either ram 41 or 27 will result in an immediate and corresponding movement of the piston of the other. Similarly, rams 42 and 28, as well as hydraulic lines extending therebetween are completely filled with hydraulic fluid so that a movement of a piston of one of the rams 42, 28 will result in an immediate and corresponding movement of the piston of the other ram. According to the preferred embodiment of this invention, the displacement of all four rams 27, 28, 41 and 42 is the same. Furthermore, the portion of the cylinder on the side of the piston containing the drive rod of the ram 27 is connected to the portion of the cylinder on the side of the piston containing the drive rod of the ram 41 by means of the first one of the pair of hydraulic lines and the other portions of the cylinders of rarns 27 and 41 are connected by the second one of the pair of hydraulic lines. Hydraulic rams 28 and 42 are connected in a similar fashion by the pair of hydraulic lines associated therewith so that all four hydraulic rams 27,- 28, 41 and 42 are balanced in terms of their relative movements in responseto a given change in pressure of the hydraulic fluid on opposite sides of the pistons thereof.

As described hereinabove, the cylinders of rams 27 and 28 are mounted on the vehicle frame andhydraulic rams 27 and 28 are connected to rocker arms 25 and 26 respectively by means of rigid lever arms 29 so that an extension of the drive rods of hydraulic rams 27 and 28 from the cylinders thereof will cause such rocker arms to rotate downwardly. The retraction of the drive rods of hydraulic rams 27 and 28 into their respective cylinders will cause rocker arms 25 and 26 to rotate upwardly as shown in FIG. 4 and described hereinabove. The drive rods of hydraulic rams 41 and 42 are pivotally attached to opposite ends of a control arm 43. The control arm 43 is mounted on the control frame 40 by means of a pivot 44 equally spaced from the ends thereof. The cylinders of the rams 41 and 42 are pivotally mounted on a guide member 45 which will be more fully described hereinafter but which may be considered to be rigidly mounted on the control frame 40 for the moment. Thus it will be seen that if the control arm 43 is pivoted about the pivot point 44 it will tend to push the drive rod of one of the hydraulic rams 41, 42 into its associated cylinder and pull the drive rod of the other ram out of its associated cylinder. Due to the hydraulic interconnection of hydraulic ram 41 with hydraulic ram 27 and the hydraulic interconnection of the ram 42 with the ram 28, corresponding movements in the drive rods of rams 27 and 28 will result. Thus the mechanical result of the mechanism thusfar described is to cause the two rocker arms 25 and 26 to operate in opposition to each other. That is, when rocker arm 25 rotates downwardly, rocker arm 26 must rotate upwardly and vice versa.

However, a more important result of the mechanism thusfar described is to insure that the force tending to cause one of the rocker arms to rotate in particular direction will be exactly equal to the force tending to cause the other rocker arm to rotate in the opposite direction. Thus, if awheel journalled in the end of rocker arm 25 is resting on the ground, whereas the wheel journalled in the end of rocker arm 26 is not touching the ground, there will be a substantial force tending to rotate the rocker arm 25 in an upward direction due to the weight of the vehicle, and a much smaller force tending torotate the rocker arm 26 in a downward direction due to solely to the weight of the wheel and the. rocker arm itself. However, the mechanism thusfar described will couple the force tending to drive the rocker arm 25 upwardly to the rocker arm.26 in such a way as to tend to drive it downwardly. For this reason, the forces throughout the system are balanced, thereby enabling the hunting and exhaustion effects in the automatic control of the system to be reduced toward a minimum.

- As shown in FIG. 4, the mechanism thusfar described is controlled by means of a control ram 46 having its cylinder pivotally mounted on the control frame 40 and its drive rod connected to the control arm 43 by means of a control lever 47. One end of the control lever 47 is rigidly attached to the control arm 43 at the point where the control arm 43 is pivotally mounted to the frame 40 and transversely to the axis of such pivotal mounting 44. The drive rod of the control ram 46 is pivotally connected to the opposite end of the control lever 47 Thus the extension and retraction of the drive rod of the control ram 46 will cause the control arm 43 to pivot about its pivotal mounting 44, pushing the drive rod of one of the rams 41, 42 into its cylinder and pulling the drive rod of the other ram out of its cylinder. Such relative motion will be hydraulically coupled to the rocker arms 25 and 26 through the rams 27 and 28 as described hereinabove.

The control ram 46 may be conveniently controlled by connecting it to the hydraulic pump and reservoir through the four-way valve 36, as shown. Thus it will be seen that the operation of the four-way valve 36 will cause the rocker arms 25 and 26 to be driven in opposite sense to each other by means of the rams 27 and 28 through the control mechanism described above. As shown in FIG. 4, the four-way valve 36 may be electrically actuated and an automatic control circuit comprising a pendulum 70 pivotally mounted on the frame of the vehicle and adapted to make electrical contact with either contact member 71 or contact member 72 if the vehicle should tip in one direction or the other. An appropriate source of electrical energy such as battery 7 3.provides the necessary energy to actuate the four-way valve 36 thereby providing an automatic control circuit which may be adapted to maintain the vehicle in a level position on horizontal or inclined terram.

The hydraulic control means 30 in accordance with this invention also enables the entire vehicle to be raised or lowered with respect to the terrain while maintaining the desired level orientation. According to the embodiment of this invention,-shown in FIG. 4, this is accomplished through the use of a furtherdoubleacting hydraulic ram 48. The cylinder of such further ram 48' is mounted on the control frame 40 and the drive rod of such further ram 48 is rigidly attached to the guide member 45. Thus the actuation of the ram 48 will cause the guide member 45 to slide back and forth within the control frame 40. Since the cylinders of both rams 41 and 42 are mounted on the guide member 45, the movement of the guide member 45 within the frame 40 will result in relative movement in the same sense between the pistons and cylinders of the rams 41 and 42, it being understood that control ram 46 will maintain a given relative position of the pistons of the rams 4l and 42 with respect to each other. Thus, as shown in FIG. 4, if the drive rod of the ram 48 is retracted, it will cause the drive rods of the rams 41 and 42 to. be further extended with respect to their respective cylinders which will in turn result in the retraction of the drive rods of rams 27 and 28 and the simultaneous rotation of rocker arms 25 and 26 in an upward direction. The extension of the drive rod of the ram 48 from its cylinder will, of course, produce an opposite result. The ram 48 is connected to the pump and reservoir of the hydraulic system through the four-way valve 37. According to the embodiment of this invention, shown in FIG. 4, the four-way valve 37 is actuated by a manual control 39 which may be a simple manuallyoperated switch to enable the control of the ram 48.

It will be seen that both four-way valves 36 and 37 may be operated simultaneously from a common hydraulic pump without upsetting the balance of forces which will exist in the system asdescribed hereinabove. It will be understood that the control frame 40 according to this embodiment of the invention need not have the box configuration described hereinabove; instead, any appropriate frame configuration providing for the mounting of the control ram 46, the control arm 43, the further ram 48 with appropriate means for guiding the guide member 45 may be used. It will be understood that such frame must be sufficiently strong to withstand a force equal to the full weight of the vehicle between the pivotal mounting 44 and the mounting of the further ram 48 to such frame. Similarly, the lever arm 47 and the frame members extending between the pivotal mounting 44 and the mounting of the control ram 46 to such members must be sufficiently strong to withstand instantaneous forces that may approach the full weight of the vehicle. Thus it will be seen that the embodiment of this invention shown in FIG. 4 will be subject to substantial mechanical wear in operation and that wear resistance of the materials used as well as the strength of such materials must be carefully taken into account in designing such embodiment.

Referring to FIGS. 5 and 6, an embodiment of this invention is shown in which problems associated with mechanical wear and mechanical strength of materials are reduced toward a minimum by the use of hydraulic mechanisms rather than mechanical mechanisms wherever possible. The hydraulic rams 27 and 28 which are connected between the frame of the vehicle and the rocker arms 25 and 26 respectively as described hereinabove are shown diagrammatically. According to this embodiment of the invention, the rams 27 and 28 are interconnected through a hydraulic control means 30 which comprises a three-stage hydraulic pump 60 of the rotary type. As shown in FIG. 6, each stageof such pump 60 comprises a pair of intermeshing gears 61 and 62. Each gear of each pair of gears is housed within a closely-fitted cylindrical cavity within the body 67 of the pump 50. The gears 61 and 62 are mounted for rotation on shafts 68 and 69. According to this embodiment of the invention, the shafts 68and 69 are common to all three stages of the pump 60. Thus one gear 61, 63, 65 of each pair of gears is mounted on shaft 68 and the other gear of each pair is mounted on shaft 69. Channels for the introduction of hydraulic fluid into each stage of the pump are provided in the body 67 of the pump. As shown in FIG. 6, such channel 66 intersects the cavities housing each pair of gears 61, 62 and is adapted to be coupled to hydraulic lines to provide for the ingress and egress of hydraulic fluid.

Referring to FIG. 5, it will be seen that the doubleacting hydraulic rams 27'and 28 are hydraulically interconnected through two stages of the three-stage hydraulic pump 60. Thus a pair of hydraulic lines 51, 52 extend from opposite ends of the cylinder of hydraulic ram 27 with the hydraulic line 51 going to one side of a first stage of the pump 60 and the hydraulic line 52 going to the opposite side of another stage of the pump 60. Since the hydraulic lines 51 and 52 go to opposite sides of their respective stages of the pump, it will be seen that the flow of hydraulic fluid induced in such lines by a movement in one direction of the piston of the ram 27 will tend to cause thegears of the pump 60 to rotate in a given direction and movement of the piston of the ram 27in the other direction will tend to cause the gears of the pump 60 to rotate in the opposite direction. Similarly, the double-acting hydraulic ram 28 is connected to the same two stages of the hydraulic pump 60 by means of hydraulic lines 53, 54 with the hydraulic line 53 being connected to the pump 60in opposition to the hydraulic line 51 and the hydraulic line 54 being connected to the pump in opposition to the hydraulic line 52. Thus it will be seen that a given rotation of the gears of the pump 60 will tend to drive the hydraulic rams 27 and 28 in opposition to each other. In other words, the rotation of the gears of the pump 60 in one direction will tend to extend the drive rod of the ram 27 and retract the drive rod of the ram 28 and rotation of the gears of the pump 60 in the opposite direction will have the opposite effect with respect to the drive rods of the rams 27 and .28. Although the stages of the pump 60 are all shown to be identical, it will be understood that the stage to which hydraulic lines 52 and 54 are connected musthave a smaller displacement than the other two stages in order to compensate for the presence of the, drive rods in the cylinders of rams 27 and 28 on the sides of the pistons thereof to which the lines 52 and 54 are connected.

The other two stages of the pump 60 preferably have 'and reservoir through the four-way valve 36. Thus,

such third stage acts as a rotary motor driving the other two stages and the direction of rotation of the pump 60 may be controlledby actuation of the four-way valve 36. Such actuation of the four-way valve may be controlled by means of an electrical control circuit 38, for example, as described in connection with FIG. 4. Thus the pistons of the rams 27 and 28 may be caused to assume a desired relative position with respectto each other within theirrespective cylinders through the action of the third stage of the pump 60 and may be locked in such relativeposition by placing the four-way valve 36 in its neutral or closed position. As with the embodiment of this invention shown in FIG. 4, it will be seen that the forces acting on the pistons 27 and 28 will be balanced, since any excess force acting on one of the rams 27 will be communicated to the other ram 28 in an opposite sense, thereby reducing the hunting and exhaustion effects described hereinabove toward 'a minimum.

According to this embodiment of the invention, ac-

cumulators 55, 6, 57, and 58 are connected'to the lines 51', 52, 53, and 54, respectively. Such accumulators are of the pressure type and function to cushion the shock which may occur during operation of the device and to provide excess hydraulic fluid to meet excessive demands which may result from such shock thereby preventing the formation of a vacuum in the system. As shown in FIG. 5, it is desirable to interpose a one-way reducing valve 59, 59' between the lines 51, 53 connected to the portion of the cylinder of each ram 27, 28 opposite the drive rod thereof and the accumulator 55, 57 associated with such line. Such one-way valve is oriented to resist the 'flow of hydraulic fluid out of the accumulator 55, 57 and thereby avoid shock reaction.

In order to operate the rams 27 and 28 in tandem rather than in opposition by the embodiment of the control means shown in FIG. 5, a pair of four-way valves 37, 37 may be used. Each one of such pair of four-way valves 37, 37' connects a different one of the rams 27 and 28 to the main pump and reservoir. As shown in FIG. 5, both four-way valves 37, 37' may be actuated-simultaneously by common control means 39. Such control means 39' may conveniently comprise a double-acting manually operated electrical switch through which a source of electric power such as a battery is connected in parallel to a pair of electri cally-a ctuated four-way valves 37, 37' as shown.

However, the second one 37 of the pair of four-way valves 37, 37" is not essential according to this embodiment of the invention since the automatic leveling system including the four-way valve 36,,control 38 and pump may be relied upon to maintain the desired relative positioning of the pistons of the rams 27, 28 with respect to each other. In other words, if a single four-way valve 37 is used it will actuate only ram 28 but such actuation will be sensed by the automatic control 38 and the ram 27 will be actuated through the pump 60, asrequired, to maintain the desired relative positioning of the rams 27, 28 with respect to each other.

It will be understood that the control device 30 according to this embodiment of the invention may be contained within an appropriateframe 40', however such frame 40 will not be subjected to any appreciable stresses during operation. It will be understood that the four-way valves and the electrical control systems couldbe included within the frame '40 which may conveniently take the form of a box housing the entire system with provision for. connecting it to the rams 27, 28 and to the main pump and reservoir. Thus the hydraulic system according to this invention may take the form of a single physical unit which may be easily incorporated into existing hydraulic systems which utilize appropriate double-acting rams such as rams 27 and Referring to FIGS. 7 and 8, a pendulum mechanism particularly suited for use in an automatic control 38 as described hereinabove as shown. The pendulum system comprises a pendulum plate 70 which, together with contact elements 71 and 72,is mounted on a base plate 73. The pendulum plate 70is mounted on the base plate 73 by means of a pivot 74 and the contact elements 71 and 72 are mounted on the base plate on opposite sides of the pendulum plate 70 and are positioned so that the pendulum plate will swing into contact with one of the elements when it pivots in one direction and into contact with the other element when it pivots in the opposite direction. An electric motor 75 is mounted on the opposite side of the pendulum plate 70 from the base plate 73 and a massive member 76 is mounted on, the shaft of the motor 75 for rotation thereby. The massive member 76 may conveniently take the form of an elongated cylinder having its axis coincident with the axis of the shaft of the motor 75.

The shaft of the motor 75 may be journalled in ap- .be understood that the rotation of the massive member 76 about its axis by the motor 75 at speeds of 10,000

revolutions per minute or more will result in gyroscopic action causing the pendulum plate to resist forces tending to cause it to pivotabout its mounting 74. Thus if the base plate 73 is mounted on the frame of a vehicle transversely thereof, the pendulum plate will tend to maintain a verticle position and the base plate 73 will pivot with respect to the pendulum plate 70, tending to bring the pendulum plate 70 into contact with one or the other of the contact elements 71 or 72. Such contact elements 71 and 72 may be simple electrical contacts as described in connection with FIG. 4. However it will be understood to those skilled in the art that such contactelements 71 and 72 may take any one 'of a number of forms. For example, they may be pressuresensitive electrical switches so that the pendulum plates 70 need not be in the electrical circuit. Similarly, they may be pressure-sensitive pneumatic or hydraulic switches.

It will be understood that the gyroscopic action described above will cause the pendulum plate 70 to resist displacement in any direction. For this reason, it may be desirable to mount the base plate 73 on the frame of the vehicle so that it may swing freely with respect to one axis of the vehicle but remain fixed with respect to the axis of the vehicle perpendicular thereto. For example, it is necessary that the vehicle tip along its longitudinal axis when climbing or descending inclined terrain, and it would be desirable for the hydraulic system disclosed herein to be insensitive to such longitudinal tipping, while reacting to transverse tipping of the frame of the vehicle. Thus the base plate 73 may be mounted on the frame of the vehicle by means of a shaft 78 having its axis transverse to the axis of both the axis of the massive member 76 and the axis of the pivot 74. Preferably, the axis of the shaft 78 should intersect the axis of the pivot 74 and the shaft 78 may be conveniently journalled in appropriate bearings 79 on opposite sides of the plate 73. Thus the gyroscopic action of the massive member 76 will maintain both the pendulum plate 70 and the base plate 73 in a vertical position in spite of longitudinal tip ping of the vehicle, whereas transverse tipping ofthe vehicle will result in relative movement between the pendulum plate 70 and the base plate 73, bringing the pendulum plate into contact with one or the other of the contact elements 71 and 72.

,As shown in FIG. 8, it would be possible to mount both the baseplate 73 and the pendulum plate 70 on a common pivot 74 which extends from the shaft 78. An appropriate manual control means could then be provided to maintain the base plate 73 in a selected position of rotation about the pivot 74 with respect to the shaft 78, thereby enabling both manual and automatic control of the hydraulic system. It will be understood that the manual control (not shown) would be used to set the base plates 73 in a selected position of rotation about the pivot 74 with respect to the shaft 78 or to change that position as desired manually. Since the pendulum plate 70 will tend to remain vertical due to gyroscopic action, such changes in the position of the base plate 73 will tend to bring the pendulum plate 70 into contact with one or the other of the contact elements 71, 72, thereby actuating the hydraulic control system. If a simultaneous change should occur with respect to the position of the transverse axis of the vehicle on which the device is mounted, further relative movement between the base plate 73 and the pendulum plate 70 will occur, assuming that the manual control means is adapted to maintain the base plate in a particular position with respect to thetransverse axis of the vehicle.

The pendulum system described above is believed to be particularly suited for use on vehicles in a hydraulic system as described hereinabove, since it will be insensitive to certain motions of the vehicle and will resist rapid changes, such as may be produced by sudden shocks, due to inertial effects and gyroscopic action, thereby further reducing the possibility of hunting effects occurring in the automatic operation of the system.

Referring again to FIGS. 4 and 5 it must be pointed out that the embodiments of the hydraulic system in accordance with this invention therein represented are shown in the one condition in which it is possible for the pendulum control 38 to provide a full range of leveling action. It will be understood that such full range of leveling action is determined by adding the maximum stroke of hydraulic ram 27 to the maximum stroke of hydraulic ram 28. Thus the maximum leveling action will be obtained when the piston of hydraulic ram 27 has moved as far as possible within the cylinder thereof in one direction and the piston of hydraulic ram 28 has moved as far as possible within the cylinder thereof in the opposite direction. As shown in FIG. 4 the pistons of hydraulic rams 27 and 28 are centrally located within the respective cylinders thereof. Similarly, the pistons of hydraulic rams 41, 42, 46 and 48 are all shown centrally located within the cylinders thereof. In this condition, if the pendulum control 38 is activated in such a way as to cause the four-way valve 36 to connect the pump and reservoir to the hydraulic cylinder 46 to drive the piston thereof to the left, it will eventually cause the piston of hydraulic ram 41 to bottom out against the bottom of the cylinder thereof and simultaneously the piston of the hydraulic ram 42 will reach the upper extremity of its possible motion. At the same time the piston of hydraulic ram 27 will move to its extreme left hand position and the piston of hydraulic ram 28 will move to its extreme right hand position thus providing the maximum possible range of leveling movement by causing the arm 25 to move to its extreme lower position and the arm 26 to move to its extreme raised position.

However, it will be seen that such full range of leveling movement can only be obtained when the piston of hydraulic ram 48 is centrally located within the cylinder thereof as shown in FIG. 4. Thus, if the control 39 is activated to cause the four-way valve 37 to connect the hydraulic ram 48 to the pump and reservoir in such a manner as to cause the piston thereof to move upwardly, the net result will be to cause the pistons of hydraulic rams 41 and 42 to assume positions closer to the bottoms thereof. Simultaneously, the pistons of hydraulic rams 27 and 28 will be caused to move closer to the extreme left-hand positions thereof moving the arms 25 and 26 closer to their extreme lower position. If the pendulum control 38 is now activated as described above, the piston of hydraulic ram 41 will bottom out against the lower end of its cylinder and the piston of hydraulic ram 27 will reach its extreme lefthand position after a shorter travel and before the piston of hydraulic ram 28 reaches its extreme righthand position or the piston of hydraulic ram 42 reaches its uppermost position. Since it is impossible for the pistons of hydraulic rams 28 and 42 to move without an opposite movement of the pistons of hydraulic rams 2'7 and 41 it will be seen that the system is immobilized as soon as the piston of one of hydraulic rams 27 or 28 reaches one of its extreme positions even though the piston of the other hydraulic ram has not reached the opposite extreme position. Thus, it will be seen that the operation of hydraulic rams 27- and. 28 in tandem to raise or lower the vehicle through the use of'control 39, four-way valve 37 and hydraulic ram 48 has the effect of reducing the leveling range obtainable according to the embodiment shown in FIG. 4.

In FIG. the pistons of hydraulic rams 27 and 28 are similarly shown centrally located in the cylinders thereof in connection with the embodiment of this invention depicted therein. Again a full range of leveling movement may be obtained through the activation of pendulum switch 38 in such a way as to cause the pistonof hydraulic ram 27 to bottom out within its cylinder and the piston of hydraulic-ram 28to move to its uppermost position within its cylinder or vice. versa. However, if the electrical switch 39 is activated to cause the pistons of cylinders 27 and 28 to move away from their central location in tandem, the leveling range obtainable through the use of pendulum switch 38 will be reduced as described inconnection with the embodiment of this invention shown in FIG. 4. Thus'as soon as the piston of one of the hydraulic cylinders 27 or 28 has reached one of its extreme positions it will lock the rotary pump 60 against further rotation thereby preventing any further movement of the piston ofthe other of hydraulic cylinders 27 or 28. v 9

It would be possible to obtain the full range of leveling action in either the embodiment shown in FIG. 4 or that shown inFIG. 5 by proper manipulation of the control 39 or 39' respectively, however, this would have to be done manually and would destroy much of the advantage of the automatic operation of pendulum switch 38.'Although it is not possible to modify the embodiment shown in FIG. 4 to overcome this disadvantage, it is possible to modify the system shown in FIG. 5 to recover the full leveling range automatically and without sacrificing the capability of the system to .on opposite sides of the lever arm 95 of the three-position valve 91' and the piston rod of hydraulic ram 28 may be provided with a pair of cam members 98 and 99 operate the hydraulic rams 27 and 28 in tandem. Such a modification isshown in FIGS. 9 and 10.

Referring to FIG. 9 it will be seen that the embodiment of this invention shown therein includes all of the elements of the embodiment of FIG. 5 except that fourway valve 37' has been omitted as suggested hereinabove in connection with FIG. 5. For ease of understanding, the same reference numerals'have been used in FIGS. 5 and 9 to indicate identical elements. The improvement of the embodiment of this invention shown in FIG. 9 over the embodiment of FIG. 5 resides in the provision of three-position valves 91 and 92 operatively associated with the pistons of hydraulic rams 27 and 28, respectively, and two-position valves 93 and 94 interposed in the hydraulic circuit between the rotary pump 60 and hydraulic'rams 27 and 28, respectively. As shown in FIG. 9 the two-position valve 93 is hydraulically controlled by the three-position valve 91 and the two-position valve 94 is hydraulically controlled by the three-position valve 92. As also indicated in FIG. 9 the three-position valve 91 is mechanically controlled by means associated with the piston of hydraulic ram 27 and three-position valve 92 is mechanically controlled by means associated with the piston of hydraulic ram 28. For example, threeposition valves 91 and 92 may each be provided with a simple lever arm 95 which is spring'loaded to cause the valves 91 and 92 to norm-ally assumea central inactive position. The piston rod of hydraulic ram 27 may be which located on opposite sides of the lever arm of threeposition valve 92. It will be understood that three-position valves 91 and 92 might be electrically, pneumatically or hydraulically operated, rather than mechanically operated, in which case the cam members 96, 97, 98, and 99 would actuate an appropriate electrical, pneumatic or hydraulic switch rather than a simple lever arm. v

According to this embodiment of the invention the three-position valves 91 and 92 are adapted hydraulically to cause the two-position valves 93 and 94, respectively, to assume the alternate position from a normal position established by spring loading of valves 93, 94, for example. In its normal position two-position valves 93connect hydraulic ram 27 to the rotary pump 60 by means of hydraulic lines 51, 51' and 52, 52' in exactly the same manner as described in'connection with FIG. 5. Similarly, in its normal position, two-posi-" tion valves .94 connects hydraulic ram 28 to rotary pump 60 by means of lines'53, 53 and 54, 54' exactly as described in connection with FIG. 5. In its alternate position, two-position valve 93 seals lines 51 and 52 and connects lines 51' and 52' to each other. Similarly, in its alternate position two-position valve 94'seals lines 53 and'54 and connects lines 53 and 54' to each other. Thus, when two-position valve 93 is actuated'by threeposition valve 91 the effect is to disconnect hydraulic ram 27 from the rotary pump 60 and at the same time provide for thecontinued rotation of rotary pump 60 independentlyof hydraulic ram 27. Similarly, the actuation of two-position valve 94 to its alternate position by three-position valve 92 serves to disconnect hydraulic ram 28 from the rotary pump and at the same'time provide for the further rotation of rotarypump 60 independently of hydraulic ram 28. As shown in FIG. 9 the input'lines to three-position valves 91 and 92 are connected to the pump and reservoir through the four-way valve 36 which is controlled by thependulum control 38. Thus, the three-position valves 91 and 92 hydraulically control the two-position valves 93 and 94 by connecting the control element thereof to the pump or to the reservoir as determined by the four-way valve 36.

The operation of the embodiment of this invention shown in FIG. 9 will be more fully understood by reference to FIG. 10 in which the hydraulic system is shown schematically using appropriate hydraulic symbols to more clearly show the functioning of the various two-position three-position and four-way valves. In FIG. 10 the reference numerals of FIG. 9 have been used to identify the schematic symbols of FIG. 10 are identical to the diagrammatically represented elements of FIG. 9. It should be noted that generalized control means 95 for three-position valves 91 and 92 are shown in place of the lever control 95 of FIG. 9. Such control means 95' may be any mechanical, electrical, pneumatic or hydraulic means adapted to be actuated by means comparable to cam surfaces 96-97 or 98-99.

As shown in FIG. 10 the piston of hydraulic ram 28 has reached the'lower extremity of its travel toward the bottom of itsassociated cylinder, whereas the piston of hydraulic ram 27 is located generally in the center of its cylinder and thus would be capable of further movement; The pendulum control 38 (not shown in FIG. has caused four-way valve 36 to assume the position which would normally cause the piston rod of hydraulic ram 27 tobe extended further and the piston rod of hydraulic ram 28 to be contracted by connecting the drive section 63 of rotary pump 60 to the pump and reservoir in such manner as to cause the upper shaft 68 thereof to rotate in a clockwise direction. Under the conditions shown the cam member 98 associated with the piston rod of hydraulic ram 28 is in contact with the control means 95 of the three-position valve 92 causing it to assume the appropriate one of its two abnormal positions to actuate two-way valve 94 by connecting the control element of two-way valve to the pump through the four-way valve 36. Such actuation of the two-way valve 94 has caused it to assume the position in which the hydraulic lines 53 and 54 are sealed and hydraulic lines 53' and 54 are connected to each other. Therefore, sections 61 and 65 of hydraulic pump 60 which are mounted on the common shaft 68 with section 63 are allowed to freely rotate thereby pumping fluid out of the upper portion of hydraulic ram 27 and into the lower portion thereof. This allows the piston of hydraulic ram 27 to continue to move in an upward direction extending the piston rod thereof independently of the fact that hydraulic ram 28 is incapable of further movement. So long as the pendulum control 38 causes the four-way valve 36 to remain in the position shown in FIG. 10, the piston of hydraulic ram 27 will continue to move until it has reached its ultimate position thereby providing the full leveling, range established by adding the length of the strokes of hydraulic rams 27 and 28.

When the piston of hydraulic ram 27 has reached the upper extremity of its travel, the cam surface 97 will contact the control means 95' associated with threeposition valve 91. Three-position valve 91 will move to the opposite alternate position from that shown for three-position valve 92 thereby connecting the hydraulic control of two-position valve 93 to the pump through the four-way valve 36. This will actuate twoway valve 93 to seal hydraulic lines 51 and 52 thereby immobilizing hydraulic ram 27 and at the same time connect hydraulic lines 51 and 52 to each other so that the pump 60 may continue to rotate in either direction independently of .both hydraulic rams 27 and 28. In this condition the hydraulic system has reached the ultimate of its operation and it will remain fixed in such position until the four-way valve 36 is moved to the opposite extreme position from that shown by action of the pendulum control 38 (not shown in FIG. 10). When this happens it will be seen that the hydraulic control means of both two-position valves 93 and 94 will be connected to the reservoir through three-position valves 91 and 92, respectively, and four-way valve 36,

thus allowing two-position valves 93 and 94 to return to their normal position and restoring the normal operation of the system (as described in connection with FIG. 5). As soon as the piston of hydraulic rams 27 and 28 move away from their extreme position, three-position valves 91 and 92 will return to their normal central position until one of the cam surfaces 96-99 again contacts one of control means 95'. It will be seen that the this invention will always tend to have its weight evenly distributed among the wheels thereof, thereby insuring that each wheel will contribute the full amount of traction in driving the vehicle of which it is capable. Furthermore, it will be seen that a vehicle equipped with the hydraulic system as described in accordance with the teaching of this invention, will tend to remain vertical along its longitudinal axis, thereby enabling the vehicle to always pass between obstacles spaced a given distance from each other regardless of the nature of the terrain between such obstacles. For example, if it is assumed that two trees are located on a sloping terrain and spaced from each other by a distance only slightly greater than the transverse distance between a pair of wheels of the vehicle, any transverse tipping of the vehicle due to the-sloping terrain would make it impossible for the vehicle to pass between the trees. Due to the action of the hydraulic system of this invention,

the vehicle will be maintained in a vertical position in spite of the sloping terrain and may therefore pass between the trees. In addition, the frame 10 of a vehicle equipped with the hydraulic system of this invention may be raised with respect to its wheels in order to clear obstructions such as stumps or large rocks lying in its path without upsetting the level orientation of the frame l0. 9

Although a vehicle embodying the hydraulic system of this invention will have particular advantages, it is believed that those skilled in the art will find many other applications for the hydraulic system of the invention, making appropriate and obvious changes in the embodiments described hereinabove in order to suit them for the particular application. The compact and unitary configuration of the hydraulic control means disclosed herein will enable it to be easily incorporated into existing hydraulic systems with little difficulty and the variety of automatic and manual controls that may be used in conjunction with the hydraulic control system described herein will readily suit it for use in many applications.

What is claimed is:

1. A hydraulic system comprising:

a. a first pair of double acting hydraulic rams;

b. mechanical means mechanically interconnecting said rams in opposition to each other;

c. hydraulic means interconnecting said rams to enable either of said pair of rams to drive the other in the opposite sense;

(I. control means controlling said hydraulic means interconnecting said rams; and

e. a source of pressurized fluid and a fluid reservoir connected to said control means, said control means enabling said rams to be driven both in tandem and in opposition, as desired, from said source of pressurized fluid and reservoir.

2. A hydraulic system as claimed in claim 1 wherein each of said first pair of double acting hydraulic rams comprises a closed cylinder and a drive rod rigidly connected to a piston contained within said cylinder; and said mechanical meansinterconnecting said ramsin opposition to each other comprises a first rigid member; the cylinders of both of said rams bearing on said first rigid member and the drive rods of both of said rams bearing on a second rigid member.

3. A hydraulic system as claimed in claim 2 wherein said hydraulic means interconnecting said first pair of rams includes a second pair of double acting rams each hydraulically connected to a different one of said first pair of hydraulic rams by a different pair of hydraulic lines, each of said hydraulic lines of said pairs of hydraulic lines extending between the cylinders on corresponding sides of the pistons of the rams associated therewith.

4. A hydraulic system as claimed in claim 3 wherein second mechanical means interconnect said. second pair of rams in opposition to each other, said second mechanical means comprising a frame, a third rigid member and a fourth rigid member, said third rigid member being pivotally mounted on said frame and said fourthrigid member being held against pivotal movement by said frame, each of said rams of said second pair of rams being mechanically connected between said third. rigid member on a different side of said pivotal mounting thereof and said fourth rigid member.

5. A hydraulic system as claimed in claim 4' wherein said control means comprises a third pair of double acting hydraulic rams each hydraulically connected to said source of pressurized fluid and fluid reservoir through a different one of a pair of four-way valves, one of said third pair of rams being mechanically connected between said frame and said third rigid member to cause pivotal movement thereof with respect to said frame when actuated and the other of said third pair of rams being mechanically connected between said fourth rigid member and said frame to cause movement thereof with respect to said frame toward and away from said pivotal mounting of said third rigid member when actuated.

6. A hydraulic system as claimed in claim 2 wherein said hydraulic means interconnecting said first pair of rams comprises a rotary fluid pump having a plurality of stages sharing a common shaft, a first hydraulic line connecting the cylinder on the side of the piston housing the drive rod of one of said pair of rams to one side I of a first stage of said pump, a second hydraulic line connecting the cylinder on the other side of the piston of said one of said pair of rams to the opposite side of a second stage of said pump, a third hydraulic line connecting the cylinder on the side of the piston housing the drive rod of the other of said pair of rams to said first stage of said pump in opposition to said first hydraulic line, and a fourth hydraulic line connecting the cylinder on the other side of said piston of said other of said pair of rams to said second stage of said pump inopposition to said second hydraulic line.

8. A hydraulic system as claimed in claim 6 wherein said control means comprises a pair of four-way valves each connected, to said source of pressurized fluid and fluid reservoir, one of said four-way valves being hydraulically connected across a third stage of said pump and the other of said valves being hydraulically connected across the cylinder of one of said pair of rams.

9. A hydraulic system as claimed in claim 8 wherein said one of said pair of fourway valves is automatically actuated to'maintain a given relative position between the pistons of said first pair of rams and one end of the cylinders thereof.

10. A hydraulic system as claimed in claim 5 wherein the four-way valve connecting said one of said third pair of rams to said source and fluid reservoir is automatically actuated to maintain a given relative position between the pistons of said second pair of rams and one end of the cylinders thereof.

11. A hydraulic system as claimed in claim l wherein the major surfaces of a flat pendulum plate for rotation about an axis parallel to said major surface, said pendulum plate being mounted on a surface of a base plate parallel to said major surface for rotation about a second axis perpendicular to said major surface and intersecting said axis of rotation of said massive member at one end of said massive member, said baseplate being mounted on a frame for rotation about a third axis intersecting said point of intersection of said axis of rotation of said massive member and said second axis transversely thereto, and a pair of contact sensing elements rigidly mounted on said surface of said base plate on opposite sides of said pendulum plate at the other endof said massive member, said contact sensing elements being spaced from said pendulum plate and adapted to be alternatively contacted thereby upon pivoting of "said third axis about said second axis in operation. I

12. A hydraulic system as claimed in claim 6 wherein a first two-position valve is interposedin said first and second hydraulic lines between one of said pair of rams and said pump and a second two-position valve is interposed in said third and fourth hydraulic lines between said other of said pair of rams and said pump, each of said first and second two-position valves having a first position in which the hydraulic lines in which it is interposed are-uninterrupted and a second position in which said hydraulic lines in which it is interposed are interrupted with the portions thereof extending between said two-position valve and said pump being connected to each other and the portions thereof extending between said two-position valve and the one of said pair of rams associated therewith being sealed.

13. A hydraulic system as claimed in claim 12 wherein said control means comprises a pair of fourway valves each connected to said source of pressurized fluid and fluid reservoir, one of said four-way valves being hydraulically connected across a third stage of said pump, the other of said valves being hydraulically connected across the cylinder of one of said pair of rams; said first and second two-position valves are hydraulically controlled; a first three-position valve is hydraulically connected between said one of said four-way valves and the hydraulic control of inactive and abnormal position which are hydraulically inverse to each other; said three-position valves being connected to said four-way valve in opposite sense from each other. 

1. A hydraulic system comprising: a. a first pair of double acting hydraulic rams; b. mechanical means mechanically interconnecting said rams in opposition to each other; c. hydraulic means interconnecting said rams to enable either of said pair of rams to drive the other in the opposite sense; d. control means controlling said hydraulic means interconnecting said rams; and e. a source of pressurized fluid and a fluid reservoir connected to said control means, said control means enabling said rams to be driven both in tandem and in opposition, as desired, from said source of pressurized fluid and reservoir.
 2. A hydraulic system as claimed in claim 1 wherein each of said first pair of double acting hydraulic rams comprises a closed cylinder and a drive rod rigidly connected to a piston contained within said cylinder; and said mechanical means interconnecting said rams in opposition to each other comprises a first rigid member; the cylinders of both of said rams bearing on said first rigid member and the drive rods of both of said rams bearing on a second rigid member.
 3. A hydraulic system as claimed in claim 2 wherein said hydraulic means interconnecting said first pair of rams includes a second pair of double acting rams each hydraulically connected to a different one of said first pair of hydraulic rams by a different pair of hydraulic lines, each of said hydraulic lines of said pairs of hydraulic lines extending between the cylinders on corresponding sides of the pistons of the rams associated therewith.
 4. A hydraulic syStem as claimed in claim 3 wherein second mechanical means interconnect said second pair of rams in opposition to each other, said second mechanical means comprising a frame, a third rigid member and a fourth rigid member, said third rigid member being pivotally mounted on said frame and said fourth rigid member being held against pivotal movement by said frame, each of said rams of said second pair of rams being mechanically connected between said third rigid member on a different side of said pivotal mounting thereof and said fourth rigid member.
 5. A hydraulic system as claimed in claim 4 wherein said control means comprises a third pair of double acting hydraulic rams each hydraulically connected to said source of pressurized fluid and fluid reservoir through a different one of a pair of four-way valves, one of said third pair of rams being mechanically connected between said frame and said third rigid member to cause pivotal movement thereof with respect to said frame when actuated and the other of said third pair of rams being mechanically connected between said fourth rigid member and said frame to cause movement thereof with respect to said frame toward and away from said pivotal mounting of said third rigid member when actuated.
 6. A hydraulic system as claimed in claim 2 wherein said hydraulic means interconnecting said first pair of rams comprises a rotary fluid pump having a plurality of stages sharing a common shaft, a first hydraulic line connecting the cylinder on the side of the piston housing the drive rod of one of said pair of rams to one side of a first stage of said pump, a second hydraulic line connecting the cylinder on the other side of the piston of said one of said pair of rams to the opposite side of a second stage of said pump, a third hydraulic line connecting the cylinder on the side of the piston housing the drive rod of the other of said pair of rams to said first stage of said pump in opposition to said first hydraulic line, and a fourth hydraulic line connecting the cylinder on the other side of said piston of said other of said pair of rams to said second stage of said pump in opposition to said second hydraulic line.
 7. A hydraulic system as claimed in claim 6 wherein said first stage of said pump has a fluid displacement which differs from the displacement of said second stage of said pump by an amount substantially equal to the difference in fluid displacement between the cylinder on the side of the piston housing the drive rod of one of said pair of rams and the cylinder on the other side of the piston of said one of said pair of rams.
 8. A hydraulic system as claimed in claim 6 wherein said control means comprises a pair of four-way valves each connected to said source of pressurized fluid and fluid reservoir, one of said four-way valves being hydraulically connected across a third stage of said pump and the other of said valves being hydraulically connected across the cylinder of one of said pair of rams.
 9. A hydraulic system as claimed in claim 8 wherein said one of said pair of four-way valves is automatically actuated to maintain a given relative position between the pistons of said first pair of rams and one end of the cylinders thereof.
 10. A hydraulic system as claimed in claim 5 wherein the four-way valve connecting said one of said third pair of rams to said source and fluid reservoir is automatically actuated to maintain a given relative position between the pistons of said second pair of rams and one end of the cylinders thereof.
 11. A hydraulic system as claimed in claim 1 wherein said control means comprises a pendulum, said pendulum comprising a massive member mounted on one of the major surfaces of a flat pendulum plate for rotation about an axis parallel to said major surface, said pendulum plate being mounted on a surface of a base plate parallel to said major surface for rotation about a second axis perpendicular to said major surface and intersecting said axis of rotation of said massive member at one End of said massive member, said base plate being mounted on a frame for rotation about a third axis intersecting said point of intersection of said axis of rotation of said massive member and said second axis transversely thereto, and a pair of contact sensing elements rigidly mounted on said surface of said base plate on opposite sides of said pendulum plate at the other end of said massive member, said contact sensing elements being spaced from said pendulum plate and adapted to be alternatively contacted thereby upon pivoting of said third axis about said second axis in operation.
 12. A hydraulic system as claimed in claim 6 wherein a first two-position valve is interposed in said first and second hydraulic lines between one of said pair of rams and said pump and a second two-position valve is interposed in said third and fourth hydraulic lines between said other of said pair of rams and said pump, each of said first and second two-position valves having a first position in which the hydraulic lines in which it is interposed are uninterrupted and a second position in which said hydraulic lines in which it is interposed are interrupted with the portions thereof extending between said two-position valve and said pump being connected to each other and the portions thereof extending between said two-position valve and the one of said pair of rams associated therewith being sealed.
 13. A hydraulic system as claimed in claim 12 wherein said control means comprises a pair of four-way valves each connected to said source of pressurized fluid and fluid reservoir, one of said four-way valves being hydraulically connected across a third stage of said pump, the other of said valves being hydraulically connected across the cylinder of one of said pair of rams; said first and second two-position valves are hydraulically controlled; a first three-position valve is hydraulically connected between said one of said four-way valves and the hydraulic control of said first two-way valve; and a second three-position valve is hydraulically connected between said one of said four-way valves and the hydraulic control of said second two-way valve; each of said three-position valves having a normal position which is hydraulically inactive and abnormal position which are hydraulically inverse to each other; said three-position valves being connected to said four-way valve in opposite sense from each other. 